1. Economy of a multiple effect evaporator depends upon the
Correct : A. Heat balance consideration
2. The main purpose of providing fins on heat transfer surface is to increase the
Correct : C. Heat transfer area
3. Wavelength corresponding to the maximum energy is inversely proportional to the absolute temperature. This is __________ law.
Correct : C. Wien's
4. Trap is used to remove __________ from steam pipe lines.
Correct : B. Condensate
5. Prandtl number is given by
Correct : C. CP µ/k
6. Pick out the wrong statement:
Correct : A. With change in temperature, the radiant energy emitted by a black body remains unchanged
7. Prandtl number is the ratio of
Correct : B. Momentum diffusivity to thermal diffusivity
8. In the free convection regime of pool boiling, the heat flux is proportional to
Correct : C. Δt5/4
9. Radiation heat losses from satisfactorily insulated high pressure boiler may be about __________ percent.
Correct : B. 7
10. When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as __________ boiling.
Correct : D. Film
11. In SI units, fouling factor is expressed in
Correct : A. m2°K/W
12. Kg of liquid evaporated per hour in an evaporator is defined as its
Correct : A. Capacity
13. The left face of a one dimensional slab of thickness 0.2 m is maintained at 80°C and the right face is exposed to air at 30°C. The thermal conductivity of the slab is 1.2 W/m.K and the heat transfer co-efficient from the right face is 10 W/m2 .K. At steady state, the temperature of the right face in °C is
Correct : D. 48.7
14. In forced convection, the heat transfer depends on
Correct : A. Re, Pr
15. Agitated film evaporator is suitable for concentrating __________ liquids.
Correct : B. Viscous
16. A composite flat wall of a furnace is made of two materials 'A' and 'B'. The thermal conductivity of 'A' is twice of that of material 'B', while the thickness of layer of 'A' is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material 'A' is
Correct : D. 160
17. Kirchoff's law is applicable to
Correct : C. Both (A) and (B)
18. The radiation heat flux from a heating element at a temperature of 800°C, in a furnace maintained at 300°C is 8 kW/m2 . The flux, when the element temperature is increased to 1000°C
for the same furnace temperature is
Correct : D. 16.5 kW/m2
19. With increase in temperature, the thermal conductivity of non-metallic amorphous solids
Correct : B. Increases
20. The Dittus-Boelter equation for convective heat transfer [(i.e. h = 0.023 (K/D) (Re) 0.8 (Pr) 0.4] cannot be used for
Correct : D. All (A), (B) and (C)
21. A black body when hot, emits heat radiation of __________ wavelengths.
Correct : C. All
22. Tube pitch is the __________ of tube diameters and the clearances.
Correct : A. Sum
23. In Joule's experiment, an insulated container contains 20 kg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighing 40 kg through a height of 4 m. The process is repeated 500 times. The acceleration due to gravity is 9.8 ms-2 . Neglecting the heat capacity of agitator, the temperature of water (in °C) is
Correct : B. 34.4
24. Heat transfer rate per unit area is called
Correct : B. Heat flux
25. The unit of heat transfer co-efficient is
Correct : A. BTU/hr. ft2°F
26. The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are
Correct : C. (COP)R = 1.5; (COP)HP = 2.5
27. For what value of Prandtl number, the Col-burn analogy is valid?
Correct : B. 0.6 to 120
28. Natural convection is characterised by
Correct : A. Grashoff number
29. Colburn analogy is applicable for the value of Prandtl number from
Correct : B. 0.6 to 120
30. A process stream of dilute aqueous solution flowing at the rate of10 Kg.s-1 is to be heated. Steam condensate at 95°C is available for heating purpose, also at a rate of 10 Kg.s-1 . A 1 - 1
shell and tube heat exchanger is available. The best arrangement is
Correct : A. Counter flow with process stream on shell side
31. The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K0 + at, where, K is the thermal conductivity and T is the temperature (in °K). The units of 'a' in SI system will be
Correct : C. W/m.k2
32. Heat exchanger tubes are never made of
Correct : C. Lead
33. Presence of a non-condensing gas in a condensing vapour
Correct : D. None of these
34. The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer coefficient
at inside of the pipe)
Correct : A. K/h0
35. Multiple effect evaporators are commonly used in the manufacture of P. Paper Q. Superphosphate R. Sugar S. Fats
Correct : C. P and S
36. In natural convection heat transfer, the correlating parameter is the
Correct : C. Grashoff number
37. Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is
Correct : B. Finned tube heat exchanger with air outside and steam inside
38. In a multiple effect evaporator, the effect of boiling point elevation is to
Correct : A. Reduce the capacity
39. Correction is applied to LMTD for __________ flow.
Correct : C. Cross
40. The heat flux in the nucleate boiling regimes is proportional to (where, ΔT = excess
temperature)
Correct : C. (ΔT)3
41. Increasing the liquor level in the evaporator results in the
Correct : A. Decreased capacity
42. In case of a vertical tube evaporator, with increase in the liquor level, the __________ is
increased.
Correct : D. Neither (A) and (B)
43. In case of a shell and tube heat exchanger, the minimum and maximum baffle spacing is
respectively (where, D = inside diameter of the shell)
Correct : A. D/5 and D
44. Pick out the wrong statement.
Correct : C. In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs
45. Double pipe heat exchangers are used
Correct : B. When heat transfer area required is very low, i.e. (100-200 ft2).
46. Sensible heat of hot industrial flue gases cannot be recovered by a/an
Correct : D. None of these
47. A body is called grey if the monochromatic emissivity of the body is
Correct : C. Same for all wavelengths
48. A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2 .°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be
Correct : B. Less than that of the un-insulated steam pipe
49. While the total emissivity of a perfect black body is unity, the same for a real body is
Correct : D. Between 0 and 1
50. In an interphase heat transfer process, the equilibrium state corresponds to equality of temperature in the two phases, while the condition for equilibrium in an interphase mass transfer process is equality of
Correct : A. Concentrations
51. Crystal size in a continuous crystalliser depends upon the
Correct : D. All (A), (B) and (C)
52. The critical radius 'r' of insulation on a pipe is given by
Correct : B. r = k/h
53. Boiling of milk in an open vessel is an example of __________ boiling.
Correct : A. Film
54. In an extended surface heat exchanger, fluid having lower co-efficient
Correct : B. Flows outside the tubes
55. Black liquor generated during paper manufacture is concentrated in a
Correct : C. Multiple effect evaporator
56. What is Nusselt number?
Correct : B. hD/k
57. If h1 = inner film co-efficient and /h2 = outer film co-efficient, then the overall heat transfer
co-efficient is
Correct : B. Always between h1 and h2
58. In the equation Q = UAΔt; Δt is
Correct : C. Logarithmic mean temperature difference
59. Convective heat transfer, in which heat is transferred by movement of warmed matter is
described by
Correct : B. Newton's law of cooling
60. For a cold dilute feed to produce thick viscous liquor, backward feeding as compared to
forward feeding results in
Correct : A. Increased economy
61. Which of the following has the minimum absorptivity?
Correct : A. Aluminium foil
62. Hot water (0.01 m3 /min) enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.05 m3 /min) of density 800 kg/m3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately
Correct : A. 32
63. In a forward feed multiple effect, the pressure build up will be
Correct : B. Least at the outlet of the last effect
64. Graetz number is given by
Correct : A. mCp/kL
65. Thermal diffusivity is given by
Correct : A. k/ρCp
66. The rate of heat transfer is a product of overall heat transfer co-efficient, the difference in temperature and the
Correct : B. Heat transfer area
67. Reynold's analogy states that
Correct : A. Nst α f
68. In case of a vertical tube evaporator, with increase in the liquor level, the
Correct : A. Capacity of the evaporator is decreased
69. Which of the following has the minimum thermal conductivity?
Correct : A. Nitrogen
70. Low thermal conductivity of heat insulating materials is due to its
Correct : B. High proportion of air space
71. For an ideal black body
Correct : A. Absorptivity = 1
72. In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD
in parallel flow to the LMTD in counter flow is always
Correct : A. < 1
73. For concentrating an aqueous solution of a material like anhydrous Na2SO4, whose solubility decreases with rise in temperature, the most suitable evaporator is a __________ evaporator.
Correct : B. Vacuum
74. Small scale evaporation is done in a
Correct : D. Steam jacketed kettle
75. Leidenfrost point is a term concerned with the
Correct : D. Boiling of a liquid on a hot surface
76. In a single effect evaporator, the economy is
Correct : B. < 1
77. At steady state the temperature variation in a plane wall, made of two different solids I &
II is shown below: The thermal conductivity of material „I‟
Correct : A. Is smaller than that of II
78. Mode of heat transfer involved in the cooling of air cooled internal combustion engine is
Correct : B. Natural convection
79. Which of the following is not used as a medium for high temperature heating ?
Correct : B. Mercury
80. In counter flow compared to parallel flow,
Correct : C. Both (A) and (B)
81. The inside heat transfer co-efficient in case of turbulent flow of liquid in the tube side in a 1-2 shell and tube heat exchanger is increased by __________ times, when the number of tube passes is increased to 8.
Correct : B. 40.8
82. Heat exchangers operating, when the asymptotic range is reached,
Correct : B. Results in making part of the heating surface inactive
83. In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred
Correct : C. By heating an intermediate material (like chequor bricks) and then heating the air from this hot material
84. In case of evaporators, liquid entrainment results primarily due to
Correct : C. Foaming of the solution
85. A multiple effect evaporator has a capacity to process 4000 kg of solid caustic soda per day,
when it is concentrating from 10% to 25% solids. The water evaporated in kg per day is
Correct : B. 24000
86. Asymptotic conditions is reached, when for a fluid flowing in laminar flow through a long
tube
Correct : C. Exit fluid temperature = wall temperature
87. The Nusselt number for fully developed (both thermally and hydrodynamically) laminar
flow through a circular pipe whose surface temperature remains constant is
Correct : C. 3.66
88. Economy of a multiple effect evaporator is not influenced much by the
Correct : A. Boiling point elevations
89. For evaporation of viscous solution in a multiple effect evaporator, the preferred feeding
scheme is
Correct : B. Backward
90. What is the absorptivity of a black body?
Correct : A. 1
91. Multiple effect evaporators ar used to
Correct : B. Increase the steam economy & the capacity
92. The average heat transfer co-efficient for laminar film condensation on vertical surface is
inversely proportional to (where, ΔT = Temperature drop across condensate film)
Correct : C. (ΔT)1/4
93. Heat transfer co-efficient (h1) for liquids increases with
Correct : A. Increasing temperature
94. Which characteristic of a fluid is not important in deciding its route in a shell and tube heat
exchanger?
Correct : D. None of these
95. Steady state one dimensional heat flow by conduction as given by Fourier's low does not
assume that
Correct : C. Material is anisotropic
96. An evaporator while concentrating an aqueous solution from 10 to 40% solids evaporates 30000 kg of water. The amount of solids handled by the system in kg is
Correct : A. 4000
97. A backward feed multiple effect evaporator is better than forward feed for concentrating
cold feed, because it provides
Correct : A. Higher economy
98. Analogy between mass and heat transfer is not applicable in case of
Correct : D. Both (B) and (C)
99. 1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m2 and the overall heat transfer co-efficient to the liquid is 1500 W/m2.°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be
Correct : D. 51 min
100. The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of
insulating material h0 = heat transfer coefficient at the outer surface)